1. Field of the Invention
The present invention relates to a multi link type piston-crank mechanism of an internal combustion engine, in which each piston of the engine and an associated crankpin of a crankshaft are connected through a plurality of links.
2. Description of the Related Art
For ease of understanding the present invention, one multi link type piston-crank mechanism hitherto proposed by the same applicants will be briefly described in the following, which is disclosed in Japanese Laid-open Patent Application (Tokkai) 2004-162895.
In the multi link type piston-crank mechanism disclosed in the publication, a lower link rotatably disposed on a crankpin of a crankshaft is connected to a corresponding piston through an upper link, and a control link is pivotally connected to the lower link to control movement of the lower link.
It has been revealed that the multi link type piston-crank mechanism of the above-mentioned publication exhibits a high freedom in setting piston stroke characteristic as compared with a single link type piston-crank mechanism in which a piston and a corresponding crank pin are connected through a single connecting rod or link. That is, in case of the multi link type, by bringing the piston stroke characteristic close to that of a simple harmonic motion (viz., sine wave), it becomes possible to reduce a vibration of the engine effectively. Furthermore, in the multi link type, by changing the position of a pivot end of the control link that is pivotally connected to a body of the engine, a compression ratio of the engine can be continuously varied while changing respective positions of TDC (viz., top dead center) and BDC (viz., bottom dead center) of the piston. That is, so-called “variable compression ratio mechanism” is readily made by such multi link type.